The present invention relates to a machine tool designed for use in adverse environments, such as for high pressure jet abrasive waterjet cutting, that has a relatively open structure to allow large workpieces to be manipulated in the structure, while maintaining a high degree of rigidity, and therefore accuracy, and having its axes being readily tightly completely sealable with bellows to prevent any possibility of contamination, even under a high pressure mist, reaching the precision bearings and ballscrews. More specifically, the invention describes an open C frame structure where the principle axes of linear motion are in a horizontal plane along the back of the C and projecting forward horizontally from the back of the C, which forms an XY motion system, and an optional vertical linear motion axes for tool height adjustment. The tool can be a high pressure waterjet nozzle, routing head, or laser beam focusing and pointing mechanism.
High pressure waterjet cutting systems evolved in the 1970s as an effective means for cutting materials ranging from delicate fabrics to wood to plastic to stone to metals (with abrasive materials in the flow stream). Most waterjet machines have been based on revolute axes-based robot systems, which tend to be inaccurate owing to the fact that angular motion joints have angular errors in them which are amplified by the robot arms' lengths. Larger systems were based on traditional machine tool designs that used conventional sealing systems for the linear axes which are not robust at resisting penetration of high pressure abrasive mists generated by the waterjet cutting process. As a result, the former type of system tended to be expensive and inaccurate, and the latter type of system tended to be expensive for maintenance. In addition, the large Cartesian machine tool systems that were designed tended to be far to large and expensive for the average job shop which actually represented the greatest business potential for waterjet cutting applications.
Other attempts to develop modular linear axes include the recent development of NSK Corporation in Japan of a modular linear motion system which they call their "monocarrier" (patent pending). This design uses an open channel shape with the linear bearings on the inside edges of the channel. The ballscrew is placed in the center of the channel and drives the carriage which is also placed in the center of the channel. The system is sealed by belt-type seals that form a sliding seal with a metal cover with longitudinal slits that covers the channel's open side. The novel feature of this design is claimed that it incorporates the bearing races directly into the structure. However, the sliding belt-type seals will have a tendency to roll dirt particles back and forth which enhances their penetration rate into the inside of the system where they will soon abrade the bearings and ballscrew. In addition, the open C shape of the system is structurally very inefficient at resisting torsional loads; hence angular (twist) errors under load will be large, and they will be amplified by the distance between the bearings and the tool tip to cause a large equivalent displacement error. This angular error amplification is known as an Abbe error and it is discussed and illustrated in detail in the textbook Precision Machine Design by Alexander H. Slocum (.RTM.1992 by Prentice-Hall, Inc. ISBN 0-13-719972-4).
Still another, and older, modular axis design is marketed by Anorad Corporation in Hauppauge New York. This system also uses an open channel structure with the linear bearing races on the inside surfaces of the channel flanges, and the carriage held between the flanges by modular linear bearings that utilize the races in the flanges, and driven by a ballscrew or linear electric motor. This system is typically sealed by a rectangular channel shaped bellows system that mates with the channel-shaped structural system. The interface between the bellows and the structure is of a sliding type which once again can be penetrated by an abrasive mist and lead to early failure of the system.
Many other types of machine, such as coordinate measuring machines and milling machines, have utilized an open C frame concept with a horizontal axis along the back of the C and a second horizontal motion axis cantilevered off of the first and projecting forward. In all of these instances, the rear horizontal axis is typically a solid member with bearings bolted in a horizontal plane to a flat surface and a rectangular channel shaped bellows for sealing. Application of this common design methodology to abrasive mist situations has led to early failures of the machines' linear motion drive components. In some large cantilevered arm gantry robots the rear horizontal axis is supported by posts, but the open channel concept has still been used which is structurally inefficient for resisting large moment loads created by the cantilevered forward projecting axis. In addition, the bellows sealing methods have been comprised of channel shaped bellows that allow abrasive mist to seep through their sliding contact interface with the axis, and the horizontal flat surface of the bellows collects abrasive dirt that abrades its way through the bellows by the contraction/expansion cycling of the bellows' folds as the axis moves.
U.S. Pat. No. 1,937,408 issued to Johnson, U.S. Pat. No. 2,007,180 issued to Doran et al., and U.S. Pat. No. 2,456,041 issued to Baker all generally disclose "open frame" type linear motion tooling machines operable by screw-type drives.
U.S. Pat. No. 3,918,331 issued to Svanstrom teaches an automatic lathe having a horizontal spindle and turret. The spindle is arranged in a spindle headstock which is rectilinearly movable in a direction perpendicular to the center line of the spindle, the turret being rectilinearly movable in a direction perpendicular to the direction of movement of the spindle headstock. The axis of rotation of the turret is perpendicular to the center line of the spindle and at least substantially parallel to the direction of movement of the spindle headstock. Turret is adapted to hold tools for internal as well as external machining operations.
U.S. Pat. No. 4,282,763 issued to Griebeler discloses an apparatus for providing oscillatory motion. The apparatus comprises drive means and an adjustable member to provide a lever of the first, second or third class, or a means having no leverage component.
U.S. Pat. No. 4,447,178 issued to Esser discloses a horizontal drilling and milling machine which comprises a vertically movable headstock and a spindle sleeve mounted for horizontal run-out from the headstock. Typically, an outer end of the spindle sleeve undergoes a vertical deflection relative to the headstock during run-out, which deflection is an exponentially function of the extent of the run-out. A correcting means is connected to the headstock to move the latter as the run-out proceeds, to effect a vertical correction displacement of the forward end of the spindle sleever, which displacement is the same exponential function of the extent of the run-out as that of the vertical deflection relative to the headstock. Correction is achieved by comparing a signal indicative of the extent of the run-out, with a predetermined exponential function for the particular spindle sleeve and tool, and generating a suitable correction signal in response thereto. A memory and computer device is employed to make the necessary comparison. The memory and computer device transmit a signal to a motor, which motor is arranged to displace a reversing roll around which a cable is extended. The ends of the cable are connected between the headstock and counterweight. Radial movement of the reversing roll causes the headstock to be inclined in a vertical plane. A motion transmitting mechanism between the motor and the reversing roll enables precise movements to be made even by a motor rotating at high rpm.
U.S. Pat. No. 4,564,995 issued to Kase discloses a composite machine tool for metal working that has a pair of vertical columns. On the front and rear sides of the vertical columns, there are provided a vertical lathe and a milling machine, respectively, able to be driven and operated independently of each other. Machining by these machine tools is effected on a workpiece rested on a pallet. A pallet transfer apparatus for conveying a succession of pallets with workpieces is provided between the vertical lathe and the milling machine and between the vertical columns. When each turning operation in the vertical lathe is finished, the corresponding pallet with the workpiece rested thereon is immediately conveyed into the milling machine by the pallet transfer apparatus. The composite machine tool is particularly useful in reducing the time for conveying comparatively heavy workpieces.
U.S. Pat. No. 4,614,128 issued to Fickler discloses a linear drive device which operates with two motors which are mounted on the outer ends of two housing parts which are locked against rotation and can be telescopically moved into each other. A motor drives a threaded rod. By means of this design, a compast drive device is procured in the case of which all mechanical parts are located inside of the housing.
U.S. Pat. No. 4,986,725 issued to Geka discloses an apparatus for transporting a machine tool such as a robot arm which comprises: upper and lower track rails each having a square or circular cross-sectional shape which are horizontally arranged in parallel so as to be away from each other in the vertical direction; and a casing slidably inserted therebetween. Rack tooth trains are formed on the lower surface of the upper track rail and on the upper surface of the lower track rail. The casing has an almost H-shaped cross-sectional shape and comprises a casing main body and two side plates attached at both end surfaces thereof. Rail side track grooves and casing side track grooves are formed on the inner wall surfaces of the track rails and casing main body. Balls are inserted between the corresponding opposite track grooves. A return passage is formed in the casing main body, ball direction turning passages are formed in the side plates, and the return passage is coupled with the casing side track grooves, thereby forming an infinity circulating passage for the balls. A pinion is rotatably arranged at the central position in the longitudinal and transversal directions of the casing main body. When the lower track rail is fixed to the fixed table and the casing main body is moved, the upper track rail moves in the same direction as the casing at the double speed.
U.S. Pat. No. 4,651,601 issued to Sasaki teaches a device for preventing a collision between a work holder and a tool in numerical control equipment for a turret punch press. A region occupied by the work holder in a mechanical coordinate system, is stored in a work holder region storing memory, and the sizes of a plurality of tool posts of a turret, or the sizes of tools received in the tool posts, are stored in a tool post shape storing memory. At the time of tool selection, a punching inhibit computing circuit computes a punching inhibit region for a selected one of the tools on the basis of the stored contents of the work holder region storing memory and the tool post shape storing memory. Immediately before the execution of a punch command, a collision preventing circuit checks whether the position of the selected tool is within the punching inhibit region or not, and if so, it stops the operation of the machine.
U.S. Pat. No. 4,987,668 issued to Roesch discloses a machine tool where the spindle of the machine-tool is mounted on a carriage movable along a horizontal transverse member which is carried by the columns of a part of the frame of the machine having the shape of a closed porch, and which is situated in front of these columns. This transverse member moves vertically along the columns. The workpiece-carrying table, which can rotate on itself, is mounted on a carriage movable in a direction parallel to the spindle axis on a portion of the frame situated in front of the porch. Thus, whatever the extreme positions of the movable elements might be, no cantilever condition is produced which could generate machine deformations.
U.S. Pat. No. 5,052,089 issued to Gadaud et al. discloses a machine tool which combines the following three features: the workpiece holder rotates around an axis which is referred to as horizontal turning axis and is parallel to one (X) of the three orthogonal axes (X, Y, Z), the said axis (C) overlying a tale the flat upper-face of which is parallel to said turning axis (C) and comprises means for fastening one or more support and/or centering means; the toolholder comprises two clamping mandrels, one for a stationary tool and the other for a rotary tool; the workpiece holder is in relation with drive means which confer upon it one of the three kinematics of the following kinematic group: immobilization in a given angular position, a so-called slow speed of rotation for milling operations which are not parallel to the axis (C), and a so-called high speed for the turning.
U.S. Pat. No. 5,154,643 issued to Catania et al. teaches a method and apparatus for positioning tooling with respect to an arc-shaped workpiece assembly spaced radially away from a centerline. The apparatus includes axially spaced apart support arm assemblies which are swingable about the centerline. Each support arm is provided with a fixed portion and a radially inwardly and outwardly movable portion, the movable portions of both arm assemblies being simultaneously movable under the control of a CNC controller. The ends of inner and outer beams are supported by the radially movable portion. Supported upon each of the inner and outer beams is a carriage assembly movable along the beam. A head is supported upon each of the carriages, each head having a relatively stationary half and a shiftable half, the shiftable half being mounted upon a track carried by the stationary half to provide for movement about a center point. In operation the beams will be swung to their position about the centerline, the carriages will be moved to their desired positions, at least one of the heads will be extended, and the tooling will be advanced towards the workpiece, all of this movement being controlled by the CNC controller. To permit loading of the apparatus, the inner beam may be split and shifted axially outwardly as the workpiece assembly is loaded.
U.S. Pat. No. 5,214,972 issued to Larson et al. discloses a linear electromechanical actuator which includes back-to-back crew-type actuators whose screw nuts are secured together. During operation, the leadscrew of one screw-type actuator is rotated whiled the leadscrew of the other screw-type actuator is locked.
A need thus exists for a machine to move a low-reaction force cutting tool, such as a water jet, laser, or high speed router, in a desired path while maintaining accuracy and environmental sealing integrity of the machine.
A need also exists for a modular machine such that a custom sized or configured machine can be easily made by merely changing the lengths of components for the axes, and bolting axes to a structural frame and to each other's moving carriages; thereby obtaining structurally rigid and accurate elements which are supported at discrete points which is a key to obtaining modular high accuracy.
A need also exists for a machine having axes that are readily completely sealable by a bellows such that no critical motion components such as the bearings, ballscrews, motors, or sensors, can be reached by a high pressure abrasive misting action from the cutting process.
A further need exists for machine axes that are most efficient in torsion so that angular errors caused by gravity loads or light reaction force loads will cause minimal angular errors which, when amplified by linear lengths of subsequently attached axes or tools will result in minimal errors at the tool-workpiece interface.
A need also exists for a machine where the linear bearings are arranged such that, when moment loads are applied to the carriage that they support, the reaction force couple on the bearings produces primarily shear stresses on the structure without creating local moments which tend to twist the axis' structure in a diaphragm mode.